AFP/ Beirut

The UN Security Council has backed a push for Syrian peace talks in a rare show of unity after widespread condemnation of regime air strikes that killed nearly 100 people.

Analysts said the vote was a sign of new resolve to address Syria's conflict, particularly as the threat of the Islamic State group grows, but cautioned that it was only a first step and vast differences between the two sides remained.

The Security Council statement, the first of its kind in two years, urges a political transition and backs a plan to create working groups to discuss ending the war.

It was approved hours after UN officials, including the organisation's peace envoy for Syria Staffan de Mistura, expressed horror at regime air strikes that killed nearly 100 people in a rebel-held town near Damascus.

On Tuesday, Syria's government hit back at de Mistura's criticism, accusing him of "making statements that lack objectivity".

The 16-point council statement backed an approach outlined by de Mistura last month after talks with parties to the four-year conflict.

It seeks to set up four working groups with members drawn from the government and opposition to discuss safety and protection, counterterrorism, political and legal issues and reconstruction.

The council urged "a Syrian-led political process leading to a political transition that meets the legitimate aspirations of the Syrian people".

- A 'first step' -

It called for "the establishment of an inclusive transitional governing body with full executive powers, which shall be formed on the basis of mutual consent while ensuring continuity of governmental institutions".

The statement made no mention of the fate of President Bashar al-Assad, whose future has long been a sticking point in talks on ending the conflict.

Assad and his backers insist he was legitimately elected and cannot be forced to step down, but the opposition insists his departure must be part of any end to the war.

The Security Council vote follows a flurry of diplomatic activity led by regime backer Moscow, which has in recent weeks hosted Syrian opposition figures as well as officials from Saudi Arabia, a key opposition backer.

The council's vote reflects "an unanimity that is unprecedented for several years," said analyst Karim Emile Bitar, a senior fellow at the IRIS think tank in Paris.

"I think it reflects a common awareness of the general state of fatigue in both parties, the fatigue and even exhaustion of both sides," he said.

But Bitar said the road ahead would not be easy and the plan represented only a "first step".

"At this stage, neither side is willing to make additional concessions that could allow this rapprochement to have concrete effects on the ground."

Syrian opposition figure Haytham Manna told AFP that efforts were already under way to find figures to serve on the four committees.

"The committees will work at their own pace and the Security Council will get involved if there are blockages and vote on resolutions when there are advances in different areas," he said.

He said the sensitive issue of Assad's future would be discussed once the committees began working, or perhaps towards the end of their talks.

- Damascus slams UN envoy -

The Security Council vote came after government air strikes on a rebel-held town outside Damascus killed nearly 100 people on Sunday, prompting widespread criticism.

The strikes on Douma, many of which hit a marketplace, were among the deadliest government attacks in the conflict.

The Syrian Observatory for Human Rights monitor said at least 96 people were killed in the strikes, which UN officials called "unacceptable".

De Mistura, speaking Monday, described the strikes as "devastating".

"Hitting crowded civilian markets killing almost one hundred of its own citizens by a government is unacceptable in any circumstances," he said.

On Tuesday, Damascus hit back at the criticism, accusing de Mistura of failing to uphold the neutrality required of his role.

"In his recent comments Staffan de Mistura has strayed from neutrality," Syrian state media said, citing a source at the foreign ministry.

The source accused de Mistura of "making statements that lack objectivity and facts and rely on what is promoted in circles known for their hostility to Syria".